Semiconductor device including high-frequency circuit with inductor

ABSTRACT

A semiconductor device with a spiral inductor is provided, which determines the area of an insulation layer to be provided in the surface of a wiring board thereunder. A trench isolation oxide film, which is a complete isolation oxide film including in part the structure of a partial isolation oxide film, is provided in a larger area of the surface of an SOI layer than that corresponding to the area of a spiral inductor. The trench isolation oxide film includes a first portion having a first width and extending in a direction approximately perpendicular the surface of a buried oxide film, and a second portion having a second width smaller than the first width and being continuously formed under the first portion, extending approximately perpendicular to the surface of the buried oxide film. The trench isolation oxide film is provided such that a horizontal distance between each end surface of the second portion and a corresponding end surface of the spiral inductor makes a predetermined distance or more.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and a method ofmanufacturing that semiconductor device, and more specifically to asemiconductor device comprising a high frequency circuit with aninductor.

2. Description of the Background Art

One example of the structure of a semiconductor device with a highfrequency circuit will be described with reference to FIG. 35. FIG. 35is a block diagram of the structure of a semiconductor device 90 thathas the function of receiving radio signals in the radio-frequency rangeof 10 kHz to 100 GHz and outputting audio signals.

As shown in FIG. 35, the semiconductor device 90 comprises at least a RFcircuit portion 91 for demodulating radio signals received, a logicportion 92 for processing and translating those signals demodulated bythe RF circuit portion 91 into audio signals, and a memory cell portion93 for storing necessary data for signal processing in the RF circuitportion 91 and the logic portion 92. The semiconductor device 90 isconnected to an antenna unit 94 for receiving radio signals and a soundoutput device 95 for outputting audio signals.

So-called high-frequency circuits, including the RF circuit portion 91,comprise an inductor (inductance element) in addition to a resistor anda capacitor. Since the inductor acts to advance the phase of highfrequency current, the use of such an inductor against the capacitorwhich acts to delay the phase of high frequency current, providesmatching of the high frequency current.

An inductor L1 in the RF circuit portion 91 illustrated in FIG. 35 has aparasitic capacitor C1 which is grounded through a resistor R1. Theresistor R1 is the resistance of a semiconductor substrate on which theRF circuit portion 91 is formed. Very low or high values of suchresistance offer no problem, but certain types of substrates have such aresistance (e.g., around 100 Ωcm) that consumes power because ofelectrostatically induced power dissipation.

FIG. 36 is a perspective view of the structure of the inductor L1. Asshown in FIG. 36, the inductor L1 is formed by winding wiring in spiralform and thus hereinafter referred to as a “spiral inductor SI”. Thecenter of the spiral, which is a first end of the spiral inductor SI, isconnected to underlying wiring WL through a contact portion CP whichpasses through an interlayer insulation film not shown.

As has been described, it is common for semiconductor devices each witha high-frequency circuit to comprise a so-called spiral inductor. Oneside of the spiral inductor has a dimension of 100 to 200 μm, and aninsulation layer whose dimensions are commensurate with those of thespiral inductor is provided in the surface of a wiring board under thespiral inductor. There is, however, a problem that the insulation layerwith an excessively large area hampers miniaturization of thesemiconductor devices, whereas the insulation layer with an excessivelysmall area makes unignorable electrostatically induced power dissipationand electromagnetically induced power dissipation due to the spiralinductor.

SUMMARY OF THE INVENTION

A first aspect of the present invention is directed to a semiconductordevice comprising: a semiconductor substrate; a first isolation oxidefilm provided in a main surface of the semiconductor substrate; and aninductance element provided on a region in which the first isolationoxide film is formed with an interlayer insulation film therebetween,wherein the first isolation oxide film is provided so that a horizontaldistance between an end surface of the first isolation oxide film and anearest one of end surfaces of the inductance element is not less than avertical distance between a lower surface of the inductance element,which is opposed to the first isolation oxide film, and a surface of thesemiconductor substrate.

A second aspect of the present invention is directed to a semiconductordevice comprising: a semiconductor substrate; a first isolation oxidefilm provided in a main surface of the semiconductor substrate; aninductance element provided on a region in which the first isolationoxide film is formed with an interlayer insulation film therebetween;and a conductor layer provided at a height between the first isolationoxide film and the inductance element; wherein the conductor layer isprovided so that a horizontal distance between an end surface of theconductor layer and a nearest one of end surfaces of the inductanceelement is not less than a vertical distance between a lower surface ofthe inductance element and a surface of the semiconductor substrate.

A third aspect of the present invention is directed to a semiconductordevice comprising: a semiconductor substrate; a first isolation oxidefilm provided in a main surface of the semiconductor substrate; aninductance element provided on a region in which the first isolationoxide film is formed with an interlayer insulation film therebetween;and a dummy pattern region provided around the first isolation oxidefilm and divided by a second isolation oxide film having a smaller widththan the first isolation oxide film in a plan view.

According to a semiconductor device of a fourth aspect of the presentinvention, the first isolation oxide film is provided so that ahorizontal distance between each end surface of the first isolationoxide film and a nearest one of end surfaces of the inductance elementis not less than a vertical distance between the lower surface of theinductance element and the surface of the semiconductor substrate.

According to a semiconductor device of a fifth aspect of the presentinvention, the semiconductor substrate is an SOI substrate comprising asubstrate portion to be a foundation, a buried oxide film provided onthe substrate portion, and an SOI layer provided on the buried oxidefilm; and the vertical distance is a vertical distance between the lowersurface of the inductance element and a surface of the substrateportion.

According to a semiconductor device of a sixth aspect of the presentinvention, the first isolation oxide film includes a first portionhaving a first width and extending in a depth direction with respect toa surface of the buried oxide film, and a second portion having a secondwidth smaller than the first width and being continuously formed underthe first portion, extending in a depth direction with respect to thesurface of the buried oxide film to reach the buried oxide film; and theend surface of the first isolation oxide film is an surface of thesecond portion.

According to a semiconductor device of a seventh aspect of the presentinvention, the first isolation oxide film has a predetermined width andextends in a depth direction with respect to a surface of the buriedoxide film.

According to a semiconductor device of an eighth aspect of the presentinvention, the first isolation oxide film is rectangular in shape in aplane view; and the dummy pattern region has a width 5% or more of alength of a short side of the first isolation oxide film.

According to a semiconductor device of a ninth aspect of the presentinvention, the dummy pattern region includes a field portion defined bythe second isolation oxide film; and an area ratio of the secondisolation oxide film in the dummy pattern region to the field portion isset to be approximately 1:1.

In the semiconductor device of the first aspect, the first isolationoxide film is provided so that the horizontal distance between each endsurface of the first isolation oxide film and a nearest one of endsurfaces of the inductance element is not less than the verticaldistance between the lower surface of the inductance element and thesurface of the semiconductor substrate. This reduces parasiticcapacitance between the inductance element and the semiconductorsubstrate in the vicinity of the end surfaces of the first isolationoxide film, resulting in a reduction in electrostatically induced powerdissipation. Further, electromagnetically induced power dissipation canbe reduced by decreasing perspective angles which are formed when theinductance element is viewed from the semiconductor substrate in thevicinity of the end surfaces of the first isolation oxide film.

In the semiconductor device of the second aspect, the conductor layer isprovided so that the horizontal distance between each end surface of theconductor layer and a nearest one of end surfaces of the inductanceelement is not less than the vertical distance between the lower surfaceof the inductance element and the substrate of the semiconductorsubstrate. This reduces parasitic capacitance between the inductanceelement and the conductor layer, resulting in a reduction inelectrostatically induced power dissipation. Further,electromagnetically induced power dissipation can be reduced bydecreasing perspective angles which are formed when the inductanceelement is viewed from the edge portions of the conductor layer.

The semiconductor device of the third aspect comprises, around the firstisolation oxide film, the dummy pattern region which is divided by thesecond isolation oxide film having a small width in the plane view.Thus, when the first isolation oxide film is formed by CMP, dishing inthe first isolation oxide film would not extend beyond the dummy patternregion. This prevents the extension of dishing to the transistorformation regions.

In the semiconductor device of the fourth aspect, electrostaticallyinduced power dissipation and electromagnetically induced powerdissipation can be reduced in either structure: the structure whereinthe conductor layer is provided at a height between the first isolationoxide film and the inductance element: and the structure wherein thedummy pattern region including the second isolation oxide film isprovided around the first isolation oxide film.

In the semiconductor device of the fifth aspect, the semiconductorsubstrate is the SOI substrate. This ensures element isolation andallows the use of a minimal width of the isolation oxide film, the widthbeing determined by micro-lithography. Thus, downsizing of the devicecan be achieved.

In the semiconductor device of the sixth aspect, the first isolationoxide film is a complete isolation oxide film including in part aso-called partial isolation oxide film. The first isolation oxide filmis comprised of a first portion having the first width and extending inthe depth direction with respect to the surface of the buried oxidefilm, and a second portion having the second width smaller than thefirst width and being formed under the first portion, extending in thedepth direction with respect to the surface of the buried oxide film toreach that buried oxide film. In such a semiconductor device thatprovides element isolation with a partial isolation oxide film,therefore, the first isolation oxide film can be formed in the processof forming the partial isolation oxide film to provide elementisolation. This simplifies the manufacturing.

In the semiconductor device of the seventh aspect, the first isolationoxide film is a so-called complete isolation oxide film which has apredetermined width and extends in the depth direction with respect tothe surface of the buried oxide film. In such a semiconductor devicethat provides element isolation with a complete isolation oxide film,therefore, the first isolation oxide film can be formed in the processof forming the complete isolation oxide film to provide elementisolation. This simplifies the manufacturing process. Further, thisfirst isolation film has no area of thin in thickness and highresistance, unlike those including in part the partial isolation oxidefilm. This allows a reduction in electromagnetically induced powerdissipation in that film.

In the semiconductor device of the eighth aspect, the dummy patternregion has the width 5% or more of the length of the short sides of thefirst isolation oxide film. This prevents dishing from extending beyondthe dummy pattern region.

In the semiconductor device of the ninth aspect, the area ratio of thesecond isolation oxide film in the dummy pattern region to the fieldportion is set to be approximately 1:1 in the plane view. Thiseffectively prevents dishing from extending beyond the dummy patternregion.

An object of the present invention is to provide a semiconductor devicewith a spiral inductor, which determines the area of an insulation layerto be provided in the surface of a wiring board under the spiralinductor.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing one example of the structure ofa semiconductor device with a spiral inductor;

FIG. 2 is a cross-sectional view showing one example of the structure ofa semiconductor device with a spiral inductor provided above a completeisolation oxide film which includes in part a partial isolation oxidefilm;

FIG. 3 is a cross-sectional view of the structure of a semiconductordevice according to a first preferred embodiment of the presentinvention;

FIG. 4 is a cross-sectional view showing clearly the features of thestructure of the semiconductor device according to the first preferredembodiment of the present invention;

FIG. 5 is a cross-sectional view illustrating the effects of thestructure of the semiconductor device according to the first preferredembodiment of the present invention;

FIGS. 6 and 7 are schematic diagrams illustrating the effects of thestructure of the semiconductor device according to the first preferredembodiment of the present invention;

FIG. 8 is a cross-sectional view of the structure of a firstmodification in the semiconductor device according to the firstpreferred embodiment of the present invention;

FIG. 9 is a cross-sectional view of the structure of a secondmodification in the semiconductor device according to the firstpreferred embodiment of the present invention;

FIG. 10 is a cross-sectional view of the structure of a semiconductordevice according to a second preferred embodiment of the presentinvention;

FIG. 11 is a cross-sectional view of the structure of a modification inthe semiconductor device according to the second preferred embodiment ofthe present invention;

FIG. 12 is a plan view illustrating connections of wiring under a spiralinductor;

FIG. 13 is a cross-sectional view illustrating the effects of dishing inan isolation oxide film;

FIG. 14 is a cross-sectional view of the structure of a semiconductordevice according to a third preferred embodiment of the presentinvention;

FIG. 15 is a cross-sectional view of the structure of a modification inthe semiconductor device according to the third preferred embodiment;

FIG. 16 is a plan view illustrating the location of a dummy patternregion;

FIG. 17 is a plan view illustrating the shape of the dummy patternregion;

FIG. 18 is a cross-sectional view of the structure of a semiconductordevice according to a fourth preferred embodiment of the presentinvention;

FIG. 19 is a schematic diagram illustrating how to reduce parasiticcapacitance;

FIG. 20 is a cross-sectional view of the structure of the semiconductordevice according to the fourth preferred embodiment of the presentinvention;

FIG. 21 is a cross-sectional view of one form of element isolation witha trench isolation oxide film;

FIGS. 22 through 26 are cross-sectional views of a method ofmanufacturing one form of element isolation with the trench isolationoxide film;

FIG. 27 is a cross-sectional view of another form of element isolationwith a trench isolation oxide film;

FIGS. 28 through 34 are cross-sectional view of a method ofmanufacturing another form of element isolation with the trenchisolation oxide film;

FIG. 35 is a block diagram showing one example of the structure of asemiconductor device with a high-frequency circuit; and

FIG. 36 is a perspective view of the structure of a spiral inductor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Introduction

Prior to descriptions of preferred embodiments of a semiconductor deviceaccording to the present invention, the structure of a semiconductordevice 90A is illustrated in FIG. 1 as one example of a semiconductordevice with a spiral inductor.

FIG. 1 shows only part of the semiconductor device 90A. Taking thesemiconductor device 90 illustrated in FIG. 35 as an example, part ofthe RF circuit portion 91 and the logic portion 92 are shown,respectively, as an RF circuit portion RP and a logic portion LP.

Referring to FIG. 1, the RF circuit portion RP and the logic portion LPare provided on an SOI substrate SB which is comprised of a siliconsubstrate 1, a buried oxide film 2 provided on the silicon substrate 1,and an SOI layer 3 provided on the buried oxide film 2.

In the RF circuit portion RP, a trench isolation oxide film 17 isprovided in an area of the SOI layer 3 that corresponds to the area of aspiral inductor SI (see FIG. 36 for the planar structure of the spiralinductor). The trench isolation oxide film 17 extends to the logicportion LP. In the logic portion LP, the SOI layer 3 is divided into twoSOI regions 71 and 72 by a trench isolation oxide film 15, and MOStransistors Q31 and Q32 are formed on the SOI regions 71 and 72,respectively.

The MOS transistors Q31 and Q32 each comprise a gate insulating film GZprovided on the SOI region 71 or 72, a gate electrode GT provided on thegate insulating film GZ, a silicide film GS provided on the gateelectrode GT, and a sidewall insulation film GW provided to cover theside faces of, respectively, the above films. These MOS transistors Q31and Q32 are of a common type with no special character in theirstructures and manufacturing method.

As for the MOS transistor Q31, there are further a silicide film SSprovided in the surface of the SOI region 71 outside the sidewallinsulation film GW, and source/drain regions SD. It is needless to saythat the MOS transistor Q32 is of the same structure, but such astructure cannot be seen just because the figure shows the cross sectionof the MOS transistor Q32 taken longitudinally of the gate electrode GT.

An interlayer insulation film 4, formed for example of a silicon oxidefilm, is provided to cover the whole surface of the SOI substrate SB,and wiring WL is provided on the interlayer insulation film 4 to providean electrical connection between the spiral inductor SI and the MOStransistor 31.

An interlayer insulation film 5, formed for example of a silicon oxidefilm, is provided to cover the surface of the interlayer insulation film4, and the spiral inductor SI is provided on the interlayer insulationfilm 5. One end of the spiral inductor SI is connected to the wiring WLthrough the contact portion CP which reaches the wiring WL through theinterlayer insulation film 5. The wiring WL is electrically connected tosemiconductor elements such as MOS transistors, but such electricalconnections are not shown in the figure.

As contrasted to the trench isolation oxide films 15 and 17 whichprovide complete electrical isolation between the SOI regions, isolationoxide films under which the SOI layer 3 is provided as a well region WRare referred to as “partial isolation oxide films”.

Partial Isolation Oxide Film

Now, a brief description of the partial isolation oxide films ispresented. In principle, the MOS transistors, each being completelyelectrically isolated from other elements by a complete isolation oxidefilm, produce no latchup with other MOS transistors.

Thus, the manufacture of SOI devices, each with CMOS transistors, usinga complete isolation oxide film has had the merit of being able to use aminimum isolation width which is determined by micro-lithography andthereby to reduce chip area. However, such SOI devices are affected bysubstrate floating body effects such as kinks in current-voltagecharacteristics due to carriers (holes for NMOS transistors) caused byimpact ionization and then stored in the channel formation region (bodyregion); degradation in operating breakdown voltage; and the dependenceof delay time on frequency because of unstable electric potential in thechannel formation region.

In this regard, the partial isolation oxide films, which are also calledpartial trench isolation, have been devised. Taking the structure ofFIG. 1 as an example, carriers are movable through the well region WRunder the partial isolation oxide film 15. This prevents carriers frombeing stored in the channel forming region and allows the electricpotential in the channel forming region to be fixed through the wellregion WR. Accordingly, no problems are caused by the substrate floatingbody effects.

Referring back to FIG. 1, the semiconductor device 90A is so constructedthat the partial isolation oxide film or trench isolation oxide film 17is provided in the area of the SOI layer 3 corresponding to the area ofthe spiral inductor SI. This is because the partial isolation oxidefilm, which is used in the logic portion LP, is also used in the RFcircuit portion RP in terms of simplification of the manufacturingprocess. However, the well region WR under the trench isolation oxidefilm 17 is thin and has high values of resistance because of its lowimpurity concentration. Thus, the parasitic capacitance C1 in theinductor L1 illustrated in FIG. 35 is grounded through the well regionWR and the value of the resistor R1 in FIG. 35 becomes high. As thevalue of the resistor R1 increases, more power is consumed byelectrostatically induced power dissipation. Further, a flow of currentthrough the spiral inductor SI produces eddy current in the well regionWR, which leads to electromagnetically induced power dissipation.

The inventors of the present invention have thus devised a structurethat will reduce electrostatically induced power dissipation andelectromagnetically induced power dissipation, by forming an oxide film,instead of the well region WR, under the trench isolation oxide film 17.

FIG. 2 shows a semiconductor device 90B with such a structure. For thesake of simplicity, only the spiral inductor SI and the structurethereunder are depicted in FIG. 2. The semiconductor device 90B is inall other aspects identical to the semiconductor device 90A in FIG. 1.The same reference numerals as in FIG. 1 designate like or correspondingparts and no mention is made here to avoid duplication.

The semiconductor device 90B in FIG. 2 is constructed such that a trenchisolation oxide film 18, which is a complete isolation oxide filmincluding in part a partial isolation oxide film, is provided in an areaof the SOI layer 3 which corresponds to the area of the spiral inductorSI.

The trench isolation oxide film 18 is comprised of a first portion 181having a first width and extending in a direction approximatelyperpendicular to the surface of the buried oxide film 2, and a secondportion 182 having a second width smaller than the first width and beingcontinuously formed under the first portion 181, extending approximatelyperpendicular to the surface of the buried oxide film 2. At least thesecond portion 182 is provided to correspond to the area of the spiralinductor SI.

With such a structure, the semiconductor device 90B can reduceelectrostatically induced power dissipation and electromagneticallyinduced power dissipation over the semiconductor device 90A in FIG. 1.In regions or edge portions X of the trench isolation oxide film 18,however, the SOI layer 3 extends under the first portion 181, formingprotrusions DP.

The protrusions DP, like the well region WR under the trench isolationoxide film 17 in FIG. 1, have high values of resistance and theinventors of the present invention had realized that electrostaticallyinduced power dissipation and electromagnetically induced powerdissipation were unignorable in such a structure. They have thusconducted an analysis of electrostatically induced power dissipation andelectromagnetically induced power dissipation and come to achieve astructure that will allow a further reduction in the above dissipation.

A. First Preferred Embodiment

<A-1. Device Structure>

Now, the structure of a semiconductor device 100 that will furtherreduce electrostatically induced power dissipation andelectromagnetically induced power dissipation is illustrated in FIG. 3as a first preferred embodiment of the semiconductor device according tothe present invention. For the sake of simplicity, only the spiralinductor SI and the structure thereunder are shown in FIG. 3. Thesemiconductor device 100 is In all other aspects identical to thesemiconductor device 90A shown in FIG. 1. The same reference numerals asin FIG. 1 designate like or corresponding parts and no mention is madehere to avoid duplication.

The semiconductor device 100 in FIG. 3 is constructed such that a trenchisolation oxide film 19, which is a complete isolation oxide filmincluding in part the structure of a partial isolation oxide film, isprovided in a larger area of the surface of the SOI layer 3 than thatcorresponding to the area of the spiral inductor SI.

Further, a silicide film 51 is provided on the main surface of the SOIlayer 3 around the trench isolation oxide film 19.

The trench isolation oxide film 19 is comprised of a first portion 191having a first width and extending in a direction approximatelyperpendicular to the surface of the buried oxide film 2, and a secondportion 192 having a second width smaller than the first width and beingcontinuously formed under the first portion 191, extending approximatelyperpendicular to the surface of the buried oxide film 2. It is providedsuch that a horizontal distance between each end surface of the secondportion 192 (i.e., the end surface of each protrusion DP of the SOIlayer 3 under the first portion 191) and the nearest end surface of aplurality of sides of the spiral inductor SI makes a predetermineddistance or more.

Here, the second portion 192 of a smaller width than the first portion191 corresponds to the structure of a complete isolation oxide film.

The details of this structure will now be described with reference toFIG. 4. FIG. 4 simplifies the structure in FIG. 3, omitting the hatchingof the trench isolation oxide film 19, and the interlayer insulationfilms 4 and 5.

Referring to FIG. 4, the horizontal distance between the end surface ofeach protrusion DP of the SOI layer 3 and the nearest end surface of thespiral inductor SI is indicated by S₀ and a distance between the lowersurface of the spiral inductor SI and the upper main surface of thesilicon substrate 1 is indicated by D₀. In FIG. 4, the aspect ratio isnot correct and so is the ratio of the distance S₀ to the size of thespiral inductor SI. To emphasize the distance S₀, the distance S₀ isshown on a larger scale than the spiral inductor SI.

The distance S₀ is set to be not less than the distance D₀ (S₀≧D₀), tothereby reduce electrostatically induced power dissipation andelectromagnetically induced power dissipation at the protrusions DP ofthe SOI layer 3.

That is, as the distance S₀ (the distance between the protrusion DP ofthe SOI layer 3 and the spiral inductor SI) increases, the parasiticcapacitance between the protrusion DP and the spiral inductor SIdecreases and electrostatically induced power dissipation are reduced.Further, electromagnetically induced power dissipation can be reduced bydecreasing perspective angles which are when the spiral inductor SI isviewed from the protrusions DP.

Description will now be made in further detail of the reduction inelectromagnetically induced power dissipation with reference to FIGS. 5through 7. FIG. 5 shows an perspective angle θ1 which is formed when thespiral inductor SI is viewed from one of the protrusions DP. Theperspective angle is defined as an angle formed by the centers of twoopposed end surfaces of the spiral inductor SI with one point at theprotrusion DP as a vertex.

FIGS. 6 and 7 schematically illustrates electromagnetically inducedpower dissipation due to the spiral inductor SI. FIG. 6 shows the casefor a relatively small perspective angle θ1; and FIG. 7 shows the casefor a relatively large perspective angle θ1, in either of which the flowof current on the two opposed sides of the spiral inductor SI areindicated by symbols.

On the right and left sides of the spiral inductor SI, the directions ofcurrent flowing at a certain moment are diametrically opposed to eachother and magnetic fields induced by such current flow on those side aredirected differently. When the perspective angle θ1 is relatively smallas shown in FIG. 6, magnetic fields MG1 and MG2 at the protrusion DP,which are established respectively by the left and right sides of thespiral inductor SI, are directed almost oppositely and cancel each otherout, thereby reducing electromagnetically induced power dissipation.This effect becomes more remarkable as the perspective angle θ1decreases, i.e., as the horizontal distance S₀ between the end surfaceof one protrusion DP and a corresponding end surface of the spiralinductor SI increases. On the contrary, larger perspective angles θ1increase electromagnetically induced power dissipation. An extreme caseis shown in FIG. 7 In FIG. 7, the end surface of one protrusion DP is atsome distance from a corresponding end surface of the spiral inductorSI, but the relative fore-and-aft positions of them are different fromthose in FIG. 6 in that the perspective angle θ1 is large. Thus, themagnetic fields MG1 and MG2 at the protrusion DP, which are establishedrespectively by the left and right sides of the spiral inductor SI, areoriented about in the same direction and intensify each other, therebyincreasing electromagnetically induced power dissipation. Here, how toreduce electrostatically induced power dissipation will be describedlater in a fourth preferred embodiment.

<A-2. Effects>

As have been described, by setting the horizontal distances S₀ betweenthe end surfaces of the protrusions DP of the SOI layer 3 andcorresponding end surfaces of the spiral inductor SI to be not less thanthe distance D₀ between the lower surface of the spiral inductor SI andthe upper main surface of the silicon substrate 1, electromagneticallyinduced power dissipation at the protrusions DP can be reduced as wellas electrostatically induced power dissipation can.

An increase in electrostatically induced power dissipation andelectromagnetically induced power dissipation will reduce the Q factor(the factor obtained by dividing energy stored in the inductor byvarious types of dissipation) which represent inductor performance. Thatis, reducing the electrostatically induced power dissipation andelectromagnetically induced power dissipation will contribute to anincrease in the Q factor, i.e., an improvement in performance, resultingin an increase in efficiency of circuitry and a reduction in noisefigure.

One example is that the distance S₀ and the distance D₀ areapproximately 8 μm and 4 μm, respectively. The distance D₀, which isdetermined by the basic structure of the semiconductor device, isdifficult to change substantially, but the distance S₀ can easily bechanged by changing the layout of the trench isolation oxide film 19.Further, since one side of the spiral inductor SI is large (about 100 to200 μm) in dimension, the whole area of the semiconductor device wouldnot extremely be increased even if the distance S₀ is somewhatincreased.

When the distance S₀ is 8 μm as above described and the spiral inductorSI has a dimension of 200 μm, for example, the area of the semiconductordevice will be increased by only about 1.2 times what it is when thedistance S₀ is 0, i.e., when the spiral inductor SI and the trenchisolation oxide film 19 have about the same area.

<A-3. First Modification>

The aforementioned semiconductor device 100 is so constructed that thetrench isolation oxide film 19, which is a complete isolation oxide filmincluding in part the structure of a partial isolation oxide film, isprovided in a larger area of the surface of the SOI layer 3 than thatcorresponding to the area of the spiral inductor SI. This trenchisolation oxide film 19 may be replaced with a trench isolation oxidefilm 20, which is a complete isolation oxide film, as illustrated in asemiconductor device 100A of FIG. 8.

In this structure, the trench isolation oxide film 20 has apredetermined width and extends approximately perpendicular to thesurface of the buried oxide film 2. The trench isolation oxide film 20is provided such that the horizontal distance between each end surfaceof the trench isolation oxide film 20 (i.e., the end surface of the SOIlayer 3) and a corresponding end surface of the spiral inductor SI makesa distance S₂.

In FIG. 8, the aspect ratio is not correct and so is the ratio of thedistance S₂ to the size of the spiral inductor SI. To emphasize thedistance S₂, the distance S₂ is shown on a larger scale than the spiralinductor SI.

By setting the distance S₂ to be not less than the distance D₀ (S₂≧D₀),the semiconductor device 100A, like the semiconductor device 100, canreduce electrostatically induced power dissipation andelectromagnetically induced power dissipation at the edge portions ofthe SOI layer 3.

In the semiconductor device 100A, the silicide film 51 is provided onthe main surface of the SOI layer 3 around the trench isolation oxidefilm 20 as in the semiconductor device 100. The silicide film 51 isformed for example by disposing a metal film such as cobalt or titaniumon the SOI layer 3 and then causing silicidation of the metal film bythe silicidation reaction. The silicide film 51 has a lower value ofresistance than the SOI layer 3 and thus current can easily flow to theground through the SOI layer 3. This further reduces electrostaticallyinduced power dissipation, thereby contributing to improvements in the Qfactor.

<A-2. Second Modification>

While the aforementioned semiconductor devices 100 and 100A are bothformed on the SOI substrates SB, it is to be understood that theapplication of the present invention is not limited to the SOIsubstrate. In fact, the present invention is applicable for example tosilicon substrates called the bulk substrate.

More specifically, as illustrated in a semiconductor device 100B of FIG.9, a trench isolation oxide film 20A may be provided in a larger area ofthe surface of a silicon substrate 10 than that corresponding to thearea of the spiral inductor SI.

In this structure, the trench isolation oxide film 20A of apredetermined with is formed almost perpendicularly in the siliconsubstrate 10. The trench isolation oxide film 20A is provided such thata horizontal distance between each end surface of the trench isolationoxide film 20A (i.e., the end surface of the silicon substrate 10) and acorresponding end surface of the spiral inductor SI makes the distanceS₂.

By setting the distance S2 to be not less than the distance D₀ (S₂≧D₀),the semiconductor device 100B, like the semiconductor device 100A, canreduce electrostatically induced power dissipation andelectromagnetically induced power dissipation at the edge portions ofthe silicon substrate 10.

B. Second Preferred Embodiment

<B-1. Device Structure>

In the structures of the aforementioned first preferred embodiment, thelayout of the trench isolation oxide film, which is provided in thesurface of the semiconductor substrate under the spiral inductor, hasbeen devised to reduce electrostatically induced power dissipation andelectromagnetically induced power dissipation in the semiconductorsubstrate in the vicinity of the interface between the semiconductorsubstrate and the trench isolation oxide film. However, it is to beunderstood that the application of the present invention is not limitedto the layout of the trench isolation oxide film. In fact, the presentinvention is also applicable to the layout of various conductor layerssuch as wiring layers.

FIG. 10 shows the structure of a semiconductor device 200 as a secondpreferred embodiment of the semiconductor device according to thepresent invention.

For the sake of simplicity, only the spiral inductor SI and thestructure thereunder are shown in the figure. The semiconductor device200 is in all other aspects identical to the semiconductor device 90Ashown in FIG. 1. The same reference numerals as in FIG. 1 designate likeor corresponding parts and no mention is made here to avoid duplication.

The semiconductor device 200 in FIG. 10 is similar to the semiconductordevice 100 illustrated in FIG. 3 in that the trench isolation oxide film19 is provided in the surface of the SOI layer 3, but it is different inthat a wiring layer WL1 is provided in an interlayer insulation film(not shown) above the trench isolation oxide film 19.

The wiring layer WL1 is provided such that a horizontal distance betweeneach end surface of the wiring layer WL1 and the nearest end surface ofthe spiral inductor SI makes the distance S₁.

In FIG. 10, the aspect ratio is not correct and so is the ratio of thedistance S₀ to the size of the spiral inductor SI. To emphasize thedistance S₀, the distance S₀ is shown on a larger scale than the spiralinductor SI.

By setting the distance S₁ to be not less than the distance D₀ (S₁≧D₀),parasitic capacitance between the wiring layer WL1 and the spiralinductor SI is reduced and thereby electrostatically induced powerdissipation is reduced. Further, electromagnetically induced powerdissipation can be reduced by decreasing perspective angles which areformed when the spiral inductor SI is viewed from the edge portions ofthe wiring layer WL.

The wiring layer WL1 may be either a metal or a polysilicon wiring layeras long as it is a conductor layer. It may also be a conductor layer,such as a dummy pattern of metal wires, which is formed in theinstallation of those metal wires. Such a dummy pattern is provided toprevent the metal wires from being too well spaced, to thereby improveplanarity when the interlayer insulation film is planarized by CMP(Chemical Mechanical Polishing) processing in such a structure that themetal wires are covered with the interlayer insulation film.

In this fashion, electrostatically induced power dissipation andelectromagnetically induced power dissipation can be reduced by avoidingas much as possible placement of layers to be conductors includingwiring layers, under the spiral inductor SI.

<B-2. Modification>

While the aforementioned semiconductor device 200 is formed on the SOIsubstrate SB, it is to be understood that the application of the presentinvention is not limited to the SOI substrate. In fact, the presentinvention is also applicable to silicon substrates called the bulksubstrate.

As illustrated in a semiconductor device 200A of FIG. 1, the trenchisolation oxide film 20A may be provided in a larger area of the surfaceof the silicon substrate 10 than that corresponding to the area of thespiral inductor SI. Then, the wiring layer WL1 may be provided in aninterlayer insulation film (not shown) on the trench isolation oxidefilm 20A so that the horizontal distance between each end surface of thewiring layer WL1 and the nearest end surface of the spiral inductor SImakes the distance S₁.

Here, it is needless to say that the distance S₁ is set to be not lessthan the distance D₀ (S₁≧D₀).

<B-3. Wiring below Spiral Inductor>

In the aforementioned structures, the placement of layers to beconductors under the spiral inductor SI is avoided as much as possible.In practice, however, the spiral inductor SI is, as shown in FIG. 10,connected to the underlying wiring WL through the contact portion CPwhich passes through an interlayer insulation film not shown. Thus, atleast the wiring WL exists under the spiral inductor SI.

In such a case, electrostatically induced power dissipation can besuppressed by locating connections between the wiring WL and otherwiring formed in other layers outside the area defined by theaforementioned distance S₁. By so doing, an increase inelectrostatically induced power dissipation, which will take place atthe connections where two or more conductor layers overlaps one another,can be prevented.

Such a structure is illustrated in FIG. 12. FIG. 12 is a plan view ofthe spiral inductor SI, wherein the dashed lines indicate the positionsthe distance S₁ away from four sides of the spiral inductor SI as awiring layout boundary region Z.

As shown in FIG. 12, the wiring WL is provided so as to extend beyondthe wiring layout boundary region Z and to be connected through acontact portion CP1 to wiring WL2 formed in a different layer.

The same applies to the other end of the spiral inductor SI. The otherend of the spiral inductor SI extends beyond the wiring layout boundaryregion Z and is connected through a contact portion CP2 to wiring WL3formed in a different layer.

C. Third Preferred Embodiment

<C-1. Device Structure>

In the structures of the first preferred embodiment according to thepresent invention, the trench isolation oxide film, which is provided inthe surface of the semiconductor device under the spiral inductor,extends over a larger area that that corresponding to the area of thespiral inductor. However, forming the trench isolation oxide film oversuch a larger area is likely to cause dishing that the trench isolationoxide film is dished out.

In the formation of the trench isolation oxide film, after a trench isformed, an oxide film is embedded in the trench and unnecessary part ofthe oxide film is removed by CMP processing. At this time, a wide-areatrench brings about too much removal of the oxide film therefrom,thereby causing dishing.

As one example of how the dishing occurs, FIG. 13 shows a structure of asemiconductor device 80. Referring to FIG. 13, in the SOI substrate SBcomprised of the silicon substrate 1, the buried oxide film 2 providedon the silicon substrate 1 and the SOI layer 3 provided on the buriedoxide film 2, a trench isolation oxide film 60 which is a partialisolation oxide film is provided in a wider area of the surface of theSOI layer 3 than that corresponding to the area of the spiral inductorSI.

There are MOS transistor formation regions QR, each with an SOI region73, on both sides of the trench isolation oxide film 60. In each of theSOI region 73, an MOS transistor Q33 is formed.

The MOS transistors Q33 each comprise a gate insulation film GZ providedon the SOI region 73, a gate electrode GT provided on the gateinsulation film GZ, and a silicide film GS provided on the gateelectrode GT. Those MOS transistor 33 are of a common type with nospecial character in their structures and manufacturing method.

The interlayer insulation film 4, formed for example of a silicon oxidefilm, is provided to cover the whole surface of the SOI substrate SB,and the wiring WL is provided on the interlayer insulation film 4 toprovide electrical connections between the spiral inductor SI and theMOS transistors Q33.

The interlayer insulation film 5, formed for example of a silicon oxidefilm, is provided to cover the surface of the interlayer insulation film4, and the spiral inductor SI is provided on the interlayer insulationfilm 5. One end of the spiral inductor SI is connected to the wiring WLthrough the contact portion CP which reaches the wiring WL through theinterlayer insulation film 5.

In the semiconductor device 80 with such a structure, the surface of thetrench isolation oxide film 60 is dished out. The upper edge portions ofsuch a trench isolation oxide film 60, where the dishing occurs, aredifferent in shape from those of normal trench isolation oxide films andmay have the adverse effects of lowering the threshold value of the MOStransistors Q33 engaged with those upper edge portions, deterioratingthe reliability of the gate insulation films GZ, and the like. There isalso a possibility that source/drain impurities may be implanted intothe channel formation region (body portion) through the thinned trenchisolation oxide film 60, thereby causing instability in transistoroperation.

As a third preferred embodiment of the semiconductor device according tothe present invention, FIG. 14 shows a structure of a semiconductordevice 300 that will prevent dishing in the trench isolation oxide filmwhich is provided over a large area. For the sake of simplicity, thespiral inductor SI and only the structure in the vicinity of the trenchisolation oxide film 19 under the spiral inductor SI are shown in FIG.14. The semiconductor device 300 is in all other aspects identical tothe semiconductor device 80 illustrated in FIG. 13. The same referencenumerals as in FIG. 13 designate like or corresponding parts and nomention is made here to avoid duplication.

Referring to FIG. 14, the trench isolation oxide film 19, which is acomplete isolation oxide film including in part the structure of thepartial isolation oxide film, is provided in a larger area of thesurface of the SOI layer 3 than that corresponding to the area of thespiral inductor SI. The structure of the trench isolation oxide film 19is illustrated in FIG. 3 and thus it is needless to say thatelectrostatically induced power dissipation and electromagneticallyinduced power dissipation can be reduced by setting the distance S₀ tobe not less than the distance D₀ (S₀≧D₀).

The SOI layer 3 around the trench isolation oxide film 19 makes a dummypattern region DMR of the trench isolation oxide film. In this dummypattern region DMR, a plurality of partial isolation oxide films PT,each having a smaller area than the trench isolation oxide film 19, areprovided to define field portions FP.

Dishing during CMP processing has the properties of noticeably occurringat and in the vicinity of wide-area field oxide films such as the trenchisolation oxide film 19 and hardly occurring in field oxide films withsmall areas. Thus, the dummy pattern region DMR, including the partialisolation oxide films PT with small areas, is provided around the trenchisolation oxide film 19. This prevents the extension of dishing to theMOS transistor formation regions QR and accordingly avoids deteriorationin MOS transistor characteristics.

<C-2. Modification>

The aforementioned semiconductor device 300 is so constructed that thetrench isolation oxide film 19, which is a complete isolation oxide filmincluding in part the structure of a partial isolation oxide film, isprovided in a larger area of the surface of the SOI layer 3 than thatcorresponding to the area of the spiral inductor SI. This trenchisolation oxide film 19 may be replaced with a trench isolation oxidefilm 20 which is a complete isolation oxide film as illustrated in asemiconductor device 300A of FIG. 15.

In this case, the trench isolation oxide film 20 is provided such thatthe horizontal distance between each end surface of the trench isolationoxide film 20 (i.e., the end surface of the SOI layer 3) and acorresponding end surface of the spiral inductor SI makes the distanceS₂. The same reference numerals as in FIG. 14 designate like orcorresponding parts and no mention is made here to avoid duplication.

By setting the distance S₂ to be not less than the distance D₀ (S₂≧D₀),the semiconductor device 300A, like the semiconductor device 100, canreduce electrostatically induced power dissipation andelectromagnetically induced power dissipation at the edge portions ofthe SOI layer 3.

The SOI layer 3 around the trench isolation oxide film 20 makes thedummy pattern region DMR of the trench isolation oxide film. In thisdummy pattern region DMR, a plurality of complete isolation oxide filmsFT, each having a smaller area than the trench isolation oxide film 19,are provided to define the field portions FP.

Further, a combination isolation oxide film BT which is a combination ofa complete isolation oxide film and a partial isolation oxide film isprovided in the interface surface between the dummy pattern region DMRand each of the MOS transistor formation regions QR. In the MOStransistor formation regions QR, partial isolation oxide films PT areprovided.

In this fashion, the dummy pattern region DMR, including the completeisolation oxide films FT with small areas and the combination isolationoxide film BT, is provided around the trench isolation oxide film 20.This prevents the extension of dishing to the MOS transistor formationregions QR and accordingly avoids deterioration in MOS transistorcharacteristics.

<C-3. Area of Dummy Pattern Region>

Now, the area of the dummy pattern region DMR will be described withreference to FIG. 16.

FIG. 16 is a plan view schematically showing the layout of the dummypattern region DMR, wherein the area of the spiral inductor SI ispresented as a rectangular inductor region SPR which is surrounded by acomplete isolation region FR of the trench isolation oxide film 19 or20. It goes without saying that the space between the solid linedefining the inductor region SPR and the dashed line defining thecomplete isolation region FR is either the aforementioned distance S₀ orS_(2.)

Further, the dummy pattern region DMR is provided to surround thecomplete isolation region FR.

The dummy pattern region DMR should preferably be set to have a width 5%or more of the length of one short side of the complete isolation regionFR. This is because the experiments by the inventors and the like hadproved that the degree of dishing during CMP processing depended on thelength of short sides of a wide-area field oxide film such as the trenchisolation oxide film 19 or 20 and that dishing would extend over 5% ormore of such a length of short sides beyond the outer edge of the trenchisolation oxide film.

Thus, by setting the dummy pattern region DMR to have the width 5% ormore of the length of the short sides of the complete isolation regionFR, the extension of dishing to the MOS transistor formation regions QRcan be prevented.

<C-4. Form of Location of Dummy Pattern Region>

Referring now to FIG. 17, one form of location of the dummy patternregion DMR will be described.

FIG. 17 is a plan view showing part of the complete isolation region FRand the dummy pattern region DMR illustrated in FIG. 16, wherein theshapes of the field portions FP in the dummy pattern region DMR areillustrated as squares in the paper plane.

The field portions FP should preferably be provided such that the arearatio of the field portions FP to an isolation oxide film (including thecomplete isolation oxide films PT, the partial isolation oxide films FT,and the like) IX therearound becomes approximately 1:1.

When the length of one side of the field portions FP is taken as 1, thearea ratio of the field portions FP to the isolation oxide film IXtherearound can be made approximately 1:1 by setting the length of oneside of the isolation oxide film IX to be 1.4.

D. Fourth Preferred Embodiment

In the structures of the first to third preferred embodiments accordingto the present invention, the trench isolation oxide film, which isprovided in the surface of tile semiconductor substrate under the spiralinductor, extends over a larger range than that corresponding to thearea of the spiral inductor. Not only that trench isolation oxide filmunder the spiral inductor but also other trench isolation oxide films tobe provided in the surface of the semiconductor device under a capacitorand a resistive element may be of the same configuration. Also in suchcases, a parasitic capacitance component and thereby electrostaticallyinduced power dissipation can be reduced.

FIG. 18 for example shows the case where the spiral inductor SI in thesemiconductor device 100 of FIG. 3 is replaced with a capacitor CC,under which the trench isolation oxide film 19 is provided.

The capacitor CC with a common structure comprises two electrodes ED1and ED2 which are connected to different wiring layers (not shown).

In FIG. 18, the horizontal distance between an end surface of eachprotrusion DP of the SOI layer 3 and a corresponding end surface of theelectrode ED1 of the capacitor CC is indicated by the distance S₀, and adistance between the lower surface of the electrode ED1 of the capacitorCC and the upper main surface of the silicon substrate 1 is indicated bythe distance D₀.

Electrostatically induced power dissipation can be reduced by settingthe distance S₀ to be not less than the distance D₀ (S₀≧D₀).

Now, the reduction in electromagnetically induced power dissipation willbe described with reference to FIG. 19. When the silicon substrate 1opposed to the electrode ED1 of the capacitor CC is taken as a virtualelectrode 1 in FIG. 19, parasitic capacitance C_(d) is generated with aninsulating material between the electrode ED1 and the virtual electrode1 as a derivative. The parasitic capacitance C_(d) can be expressed bythe following equation (1): $\begin{matrix}{C_{d} \propto {ɛ\frac{1}{D_{0}}}} & (1)\end{matrix}$

where ε is the permittivity of the dielectric.

On the other hand, when one protrusion DP of the SOI layer 3 is taken asan electrode against the electrode ED1 of the capacitor CC, parasiticcapacitance C_(S) is created with an insulating material between theprotrusion DP and the electrode ED1 of the capacitor CC as a dielectric.In this case, a linear distance between the protrusion DP of the SOIlayer 3 and the electrode ED1 of the capacitor CC can be expressed bythe square root of S₀ ²+D₀ ² and the parasitic capacitance C_(S) can beexpressed by the following equation (2): $\begin{matrix}{C_{s} \propto {ɛ\frac{1}{\sqrt{S_{0}^{2} + D_{0}^{2}}}}} & (2)\end{matrix}$

For the distance S₀ of 0 (i.e., with a conventional structure), theparasitic capacitance C_(S) is equal to the parasitic capacitance C_(d);therefore, the total parasitic capacitance is twice as much as theparasitic capacitance C_(d). In the present invention, the distance S₀is not less than the distance D₀. Thus, when S₀=D₀ for example, theparasitic capacitance C_(S) can be expressed by the following equation(3): $\begin{matrix}{C_{s} \propto {ɛ\frac{1}{D_{0}\sqrt{2}}}} & (3)\end{matrix}$

As can be seen from the equation (3), the parasitic capacitance C_(S)equals {fraction (1/{square root}{square root over (2)})} of theparasitic capacitance C_(d). The parasitic capacitance can thus besmaller than that in conventional cases, which results in a reduction inelectrostatically induced power dissipation.

This mechanism also applies to the first to third preferred embodiments.

FIG. 20 shows the case where the spiral inductor SI in the semiconductordevice 100 of FIG. 3 is replaced with a resistive element RE, underwhich the trench isolation oxide film 19 is provided.

The resistive element RE with a common structure has its two endsconnected to different wiring layers (not shown).

In FIG. 20, a horizontal distance between the end surface of eachprotrusion DP of the SOI layer 3 and a corresponding end surface of theresistive element RE is indicated by the distance S₀, and a distancebetween the lower surface of the resistive element RE and the upper mainsurface of the silicon substrate 1 is indicated by the distance D₀.

As have been described, electrostatically induced power dissipation canbe reduced by setting the distance S₀ to be not less than the distanceD₀ (S₀≧D₀).

Further as in the third preferred embodiment, it goes without sayingthat the extension of dishing to the MOS transistor formation regionsand thereby deterioration in MOS transistor characteristics can beprevented by providing the dummy pattern region around the trenchisolation oxide film 19.

E. Forms of Element Isolation with Various Trench Isolation Oxide Films

In the foregoing description, the trench isolation oxide film as acomplete isolation oxide film including in part the structure of apartial isolation oxide film is illustrated in FIG. 2; and thecombination isolation oxide film BT which is a combination of a completeisolation oxide film and a partial isolation oxide film is illustratedin FIG. 27. Now, one example of the configuration of element isolationand its manufacturing method using the above trench isolation oxidefilms will be described.

<E-1. First Form>

FIG. 21 shows the structure of a semiconductor device 400 that provideselement isolation with a complete isolation oxide film including in partthe structure of a partial isolation oxide film. A trench isolationoxide film 33 illustrated therein corresponds to the trench isolationoxide film 19 described in the first preferred embodiment.

Referring to FIG. 21, in the semiconductor device having the SOIstructure comprised of the silicon substrate 1, the buried oxide film 2,and the SOI layer 3, each transistor formation region in the SOI layer 3is divided by a partial isolation oxide film 31 with a well regionformed thereunder. A p-type well region 11 is formed under the partialisolation oxide film 31 which provides isolation between NMOStransistors, and an n-type well region 12 is formed under the partialisolation oxide film 31 which provides isolation between PMOStransistors. Isolation between the PMOS transistors and the NMOStransistors is achieved by the trench isolation oxide film 33. Thetrench isolation oxide film 33 has well regions 29 in part of the lowerportion but in most parts extends from the top to the bottom surfaces ofthe SOI layer 3 to provide complete isolation between the PMOStransistors and the NMOS transistors.

The well region 11 is formed to surround drain and source regions 5 and6 of the NMOS transistor group, and the well region 12 is formed tosurround drain and source regions 5 and 6 of the PMOS transistor group.The surface of the SOI layer 3 is covered with the interlayer insulationfilm 4.

A single MOS transistor isolated from others by the partial isolationoxide film 31 comprises the drain region 5, the source region 6, achannel formation region 7, those regions 5, 6, 7 being formed in theSOI layer 3, a gate oxide film 8 formed on the channel formation region7, and a gate electrode 9 formed on the gate oxide film 8. A wiringlayer 22 formed on the interlayer insulation film 4 is electricallyconnected to the drain or source region 5, 6 through a contact 21 formedin the interlayer insulation film 4.

Referring now to FIGS. 22 through 26, the element isolation process inthe semiconductor device 400 will be described.

First, the SOI substrate SB comprised of the silicon substrate 1, theburied oxide film 2, and the SOI layer 3 is prepared as shown in FIG.22. Normally, the SOI layer 3 has a thickness of 50 to 200 nm, and theburied oxide film 2 has a thickness of 100 to 400 nm.

The SOI substrate SB may be formed by any method such as the SIMOXmethod to form the buried oxide film 2 by oxygen ion implantation, thewafer bonding method, or the like. The present invention imposes nolimitations upon the method of manufacturing the SOI substrate SB.

Then, an oxide film 41 having a thickness of about 20 nm and a nitridefilm 42 having a thickness of about 200 nm are deposited on the SOIsubstrate 3 in that order. A subsequent patterning of the isolationregion using a patterned resist 43 as a mask etches a three-layer filmcomprised of the nitride film 42, the oxide film 41 and the SOI layer 3so that the lower portion of the SOI layer 3 is left. This providesrelatively wide partial trenches 44A and relatively narrow partialtrenches 44B as shown in FIG. 23.

The partial trenches 44A are used for complete isolation and the partialtrenches 44B for partial isolation. The partial trenches 44A and 44B areformed so that the lower portion of the SOI layer 3 is left.

Then as shown in FIG. 24, oxide films 47 are formed as sidewalls on theside surfaces of the partial trenches 44A and 44B so that the bottomsurfaces of the partial trenches 44B are covered with those sidewallsbut the bottom center portions of the partial trenches 44A are exposed.This utilizes the fact that the width of the partial trenches 44B isless than that of the partial trenches 44A.

Using the oxide films 47 as masks, silicon etching is performed on theSOI layer 3 as shown in FIG. 25. Accordingly, part of the SOI layer 3which is not covered with the oxide films 47, including the portionsunder the bottom center portions of the partial trenches 44A, is removedand part of the surface of the buried oxide film 2 is exposed.

After an oxide film having a thickness of about 500 nm is deposited,polishing is performed through CMP processing in a similar manner to theconventional trench isolation so that the nitride film 42 is removedpartway. Then, the nitride film 42 and the oxide film 41 are removed toobtain the structure as shown in FIG. 26, wherein the partial isolationoxide films 31 (and the SOI layer 3 thereunder) and the trench isolationoxide films 33 (and the SOI layer 3 under part thereof) are selectivelyformed.

Thereafter, NMOS transistors and PMOS transistors are formed in the NMOStransistor formation region and the PMOS transistor formation region,respectively, by the existing method. This completes the semiconductordevice 400 shown in FIG. 7.

<E-2. Second Form>

FIG. 27 shows the structure of a semiconductor device 500 that provideselement isolation with a combination isolation oxide film which is acombination of a complete isolation oxide film and a partial isolationoxide film. A combination isolation oxide film BT1 illustrated thereincorresponds to the combination isolation oxide film BT described as onemodification in the third preferred embodiment.

As shown in FIG. 27, the semiconductor device 500 is formed on the SOIsubstrate SB with the buried oxide film 2 and the SOI layer 3 providedon the silicon substrate 1. The device 50 has a region NR to form NMOStransistors and a region PR to form a PMOS transistor, between whichthere is the combination isolation oxide film BT1 which is a combinationof a complete isolation oxide film and a partial isolation oxide film.

The sectional shape of the combination isolation oxide film BT1 is suchthat the portion on the region PR side reaches the buried oxide film 2through the SOI layer 3 while the portion on the region NR side has ap-type well region WR1 thereunder.

On the SOI layer 3 in the region NR, two NMOS transistors M11 and M12are provided and isolated from each other by a partial isolation oxidefilm PT1 with the well region WR1 provided thereunder.

The NMOS transistor M11 provided on the left side of the partialisolation oxide film PT1 on the SOI layer 3 comprises a gate oxide filmGO11 extending between the partial isolation oxide film PT1 and anothercombination isolation oxide film BT1, and a gate electrode GT11 providedon the gate oxide film GO11 with its ends engaged on top of the partialisolation oxide film PT1 and the other combination isolation oxide filmBT1.

The NMOS transistor M12 provided on the right side of the partialisolation oxide film PT1 on the SOI layer 3 comprises a gate oxide filmGO12 extending between the partial isolation oxide film PT1 and thecombination isolation oxide film BT1, and a gate electrode GT12 providedon the gate oxide film GO12 with its ends engaged on top of the partialisolation oxide film PT1 and the combination isolation oxide film BT1.

Further, a partial isolation oxide film PT2 is provided in the SOI layer3 in the region PR, and a PMOS transistor M13 is provided on the SOIlayer 3 between the partial isolation oxide film PT2 and the combinationisolation oxide film BT1.

The PMOS transistor M13 comprises a gate oxide film GO13 extendingbetween the partial isolation oxide film PT2 and the combinationisolation oxide film BT1, and a gate electrode GT13 provided on the gateoxide film G013 with its ends engaged on top of the partial isolationoxide film PT2 and the combination isolation oxide film BT1.

Then, an interlayer insulation film 9 is provided across the surface ofSOI substrate SB, and a plurality of gate contacts GC are provided eachto reach one end of any of the gate electrodes GT11, GT12 and GT13through the interlayer insulation film 9. The gate contacts GS areconnected to wiring layers WL0 patterned on the interlayer insulationfilm 9.

Referring now to FIGS. 28 through 34, the element isolation process inthe semiconductor device 500 will be described.

First, the SOI substrate SB with the buried oxide film 2 and the SOIlayer 3 provided on the silicon substrate 1 is prepared as shown in FIG.28. The SOI substrate SB may be formed by any method such as the SIMOXmethod, the wafer bonding method, or the like. Normally, the SOI layer 3has a thickness of 50 to 200 nm, and the buried oxide film 2 has athickness of 100 to 400 nm.

An oxide film (oxide extension layer) OX11 of about 5 to 50 nm (50 to500 Å) in thickness is formed on the SOI layer 3 by CVD under atemperature condition of about 800° C. Alternatively, the oxide filmOX11 may be formed by thermal oxidization of the SOI layer 3 under atemperature condition of about 800 to 1000° C.

Then, a polysilicon layer (oxide extension layer) PS11 of about 10 to100 nm (100 to 1000 Å) in thickness is formed on the oxide film OX11 byCVD.

Further, a nitride film SN11 of about 50 to 200 nm (500 to 2000 Å) inthickness is formed on the polysilicon layer PS11 by CVD under atemperature condition of about 700° C. The nitride film may be replacedwith an oxynitride film which is formed in a mixed atmosphere ofnitrogen and oxygen to contain several to several tens percent nitrogen.

Following this, a resist mask RM1 is formed on the nitride film SN11 bypatterning. The resist mask RM11 has such a pattern that openings areformed in portions corresponding to the locations of the partialisolation oxide films PT1 and PT2 and the combination isolation oxidefilm BT1 (FIG. 1).

In the step shown in FIG. 29, the nitride film SN11 is etched accordingto the opening pattern of the resist mask RM11. With the etched nitridefilm SN11 as an etching mask, the polysilicon layer PS11, the oxide filmOX11, and the SOI layer 3 are selectively removed by dry etching, tothereby form trenches TR1, TR2 and TR3 in positions corresponding tothose of the partial isolation oxide films PT1 and PT2 and thecombination isolation oxide film BT1.

The etching process on the SOI layer 3 must not proceed to the extentthat the surface of the buried oxide film 2 is exposed. Further, crystaldefects will occur if the SOI layer 3 between the bottoms of thetrenches TR1 to TR3 and the surface of the buried oxide film 2 isexcessively thin. Thus, the etching condition should be set that theetched SOI layer 3 has a thickness of at least about 10 nm.

In the step shown in FIG. 30, a resist mask RM12 is formed bypatterning. The resist mask RM12 has such a pattern that only apredetermined portion of the trench TR2 makes an opening. Morespecifically, the pattern of the resist mask RM12 is such that only anarea of the to-be-formed combination isolation oxide film BT1 (FIG. 27)which reaches the buried oxide film 2 through the SOI layer 3 makes anopening. The trench TR2 is then etched according to the opening patternof the resist mask RM12, whereby the buried oxide film 2 is exposed.

After the resist mask RM12 is removed, in the step shown in FIG. 31, theexposed surface of the SOI layer 3 is thermally oxidized with thenitride film SN11 as a mask, to thereby form an oxide film OX12.Subsequent re-etching of the trench TR2 forms a trench TR21, part ofwhich passes through the SOI layer 3.

Forming the oxide film OX12 is for the purpose of avoiding damage causedby etching for the patterning of the SOI layer 3 and of obtaining gateoxide films that will improve reliability through the prevention ofdielectric breakdown.

The oxide film OX12 is formed to a thickness of about 1 to 60 nm (10 to600 Å) at a temperature of about 800 to 1350° C. Annealing may beperformed at least either before or after oxidation in any of nitrogen,hydrogen, and argon atmosphere. As an annealing condition, the treatmenttime is about 30 minutes to two hours for a relatively low temperatureof 600 to 900° C. and is about two seconds to one minute for arelatively high temperature of 900 to 1300° C.

The annealing before oxidation can improve crystallinity of theoutermost surface of the SOI layer 3, whereas the annealing afteroxidation can relax stresses applied onto the SOI layer 3 by heattreatment.

In the step shown in FIG. 32, an oxide film OX13 of about 300 to 600 nmin thickness is formed across the SOI substrate SB by CVD, to completelyfill the trenches TR1, TR3 and TR21 with the oxide film OX13.

The oxide film OX13 is formed by HDP-CVD (high density plasma-CVD), forexample. The HDP-CVD, which employs plasma with its density one or twodigits higher than that in general plasma CVD, is to deposit an oxidefilm while performing sputtering and deposition simultaneously. Thisprovides an oxide film of excellent film quality.

The oxide film OX13 has irregularities that reflect differences in levelamong the trenches TR1, TR3, TR21, and the like. To cover suchirregularities, a patterned resist mask RM13 is formed on the oxide filmOX13.

The oxide film OX13 is etched to a predetermined depth according to theopening pattern of the resist mask RM13 and thereafter the resist maskRM13 is removed. This provides the structure illustrated in FIG. 33. Thereason for performing such processing is to improve uniformity in thethickness of the oxide film OX13 after planalization which will beperformed in later CMP (chemical mechanical polishing) processing.

In the step shown in FIG. 34, the oxide film OX13 is polished to themiddle of the nitride film SN11 by CMP for planarization. Then, thenitride film SN11 and the polysilicon layer PS11 are removed by wet ordry etching, to thereby form the partial isolation oxide films PT1 andPT2 and the combination isolation oxide film BT1 shown in FIG. 27.

Thereafter, NMOS transistors and PMOS transistors are formed in the NMOStransistor formation region NR and the PMOS transistor formation regionPR, respectively, by existing methods. This completes the semiconductordevice 500 shown in FIG. 27.

An example of the combination of a complete isolation oxide film and apartial isolation oxide film and its manufacturing method are disclosedfor example in the specification of Japanese Patent Application No.11-177091 (1999) along with the drawings, namely, FIGS. 4-7 and 8-27.The entire disclosure of the above Japanese Patent Application No.11-177091 (U.S. patent application, Ser. No. 09/466,934 filed Dec. 20,1999) is herein incorporated by reference.

Further, the structure of the combination isolation oxide film and itsmanufacturing method are disclosed in the specification of JapanesePatent Application No. 2000-39484 along with the drawings, namely, FIGS.1-38. The entire disclosure of the above Japanese Patent Application No.2000-39484 (U.S. patent application, Ser. No. 09/639,953 filed Aug. 17,2000) is herein incorporated by reference.

While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous modifications andvariations can be devised without departing from the scope of theinvention.

What is claimed is:
 1. A semiconductor device comprising: asemiconductor substrate; a first isolation oxide film provided in a mainsurface of said semiconductor substrate; and an inductance elementprovided on a region in which said first isolation oxide film is formedwith an interlayer insulation film therebetween, wherein said firstisolation oxide film is provided so that a horizontal distance betweenan end surface of said first isolation oxide film and a nearest one ofend surfaces of said inductance element is not less than a verticaldistance between a lower surface of said inductance element, which isopposed to said first isolation oxide film, and a surface of saidsemiconductor substrate.
 2. The semiconductor device according to claim1, wherein: said semiconductor substrate is an SOI substrate comprisinga substrate portion to be a foundation, a buried oxide film provided onsaid substrate portion, and an SOI layer provided on said buried oxidefilm; and said vertical distance is a vertical distance between thelower surface of said inductance element and a surface of said substrateportion.
 3. The semiconductor device according to claim 2, wherein: saidfirst isolation oxide film includes a first portion having a first widthand extending in a depth direction with respect to a surface of saidburied oxide film, and a second portion having a second width smallerthan said first width and being continuously formed under said firstportion, extending in a depth direction with respect to said surface ofsaid buried oxide film to reach said buried oxide film; and said endsurface of said first isolation oxide film is an end surface of saidsecond portion.
 4. The semiconductor device according to claim 2,wherein said first isolation oxide film has a predetermined width andextends in a depth direction with respect to a surface of said buriedoxide film.